Question
The difference between the two acute angkes of a right angles triangle is $\frac{2\pi}{5}$ redians. Express the angles in degrees.

Answer

Let $\theta_{1}$ and $\theta_{2}$ be two acute angles of a right angles triangle.
$\therefore$ Difference of acute angles.
$\theta_{1}-\theta_{2}=\frac{2\pi}{5}\ \text{radians}$
$\therefore$ In a right angled triangle,
$\theta_{1}+\theta_{2}=\frac{\pi}{2}$
 $\theta_{1}+\theta_{2}=\frac{2\pi}{5}$
$\theta_{1}+\theta_{2}=\frac{\pi}{2}$
On solving
$2\theta_{1}=\frac{2\pi}{5}+\frac{\pi}{2}$
$\theta_{1}=\frac{9\pi}{20}$
From quation (ii)
 $\theta_{2}=\frac{\pi}{20}$
So angles in degrees,
 $\theta_{1}=\frac{9\pi}{20}\times\frac{180}{\pi}=81^{\circ}$
 $\theta_{2}=\frac{\pi}{20}\times\frac{180}{\pi}=9^{\circ}$

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